Method of roasting and reducing ores



METHOD OF ROASTING AND REDUCING ORES Filed larch 29, 1926 czgcrrq IL ll#1 ll 00 OCT (5,

GOOD

Patented Aug. 14, 1928.

PATENT OFFICE.

BROR CHBiISTIANSEN, OF SMEDJ'EBACKEN, SWEDEN.

METHOD OF BOASTING AND REDUCING ORES.

Application filed March 29, 1928, Serial No. 98,347, and in Sweden April7, 1925.

This invention relates to an improved method of roasting and reducingores in a channel furnace through which the ore charged on carriages orthe like is successively moved. The method is especially adapted forproducing spongy iron of fine iron ores but it can also be used for thereduction of other iron ores as well as the ores of other metals. I

The chief object of the invention is to provide an improved reductionmethod of said kind by which the ore can be roasted and reduced in asingle operation in a simple manner and at low cost.

The invention consists, chiefly, in first introducing'the ore in.apreheating and roasting zone of the channel furnace where combustion ofgaseous fuel takes place by means of an excess of air so that the ore ispreheated and roasted, then transferring the ore to a prereduction zonewherein it is acted upon by a reducing atmosphere containing carbonmonoxide, and finally transferring the ore into a reduction zoneseparated from the prereduction zone through which gases consistingchiefly of carbon monoxide are circulated, said gases being outside thereduction furnace regenerated by means of an incandescent layer ofcarbon, the excess of gas formed inthe circulation system being whollyor partly utilized for the prereduction of the ore in the prereductionzone and finally combusted in the roast-ing zone.

In the accompanying drawmgs I have shown diagrammatically in Fig. 1 alongitudinal vertical section of channel furnace adapted for theproducing of spongy iron according to this invention. Fig. 2 is ahorizontal longitudinal section of the furnace.

Referring to the drawings, A is the introduction end of the channelfurnace and B isthe discharge end. Nearest to the introduction end A isa preheating zone C and then a roasting zone D and a prereduction zone Efollow.. Through the introduction end carriages b made of refractorymaterial and loaded with the ore to be treated are successivelyintroduced into the furnace. The ore loaded on the carriages ispreferably in the form of pressed cakes or blocks. When a carriage is tobe introduced a shutter a at the introduction end is opened and theloaded carriage pushed into the furnace while the whole'row of carriagesis moved one step forwards, whereupon the shutter a is immediatelyclosed. Combus tible gas is supplied through a pipe at 'I, said gasbeing obtained from the recarboniz ing furnaces described herebelow, andat F an excess of preferably preheated air is supplled by means of whichthe gas supplied at T is combusted in the zone D whereupon thecombustion gases pass the zone C and escape through the chimney I. Inthe zone C a preheating of the ore takes place by the hot combustiongases and the temperature of the ore rises the nearer the carriages cometo the inner end of the zone D. By this preheating the ore cakes are inwellknown manner converted into rather hard briquettes. As air ispresent in the zones D, C in excess the ore is simultaneously roasted,the sulphur in the ore being oxidized into sulphurous acid which escapestogether with the combustion gases. If the ore consists of magnetite (FeO it is also oxidized into Fe O which is profitable for the followingreduction process. The temperature in the zone D should be kept as highas possible without the ore being smelted or sintered. WVhen treatingores which are not easily fusible the temperature inthe zone D can beraised up to 1400 to 1450 C.

The inner end of the combustion zone D is in direct communication withthe prereduction zone E. When the desulphurized and oxidizedincandescent briquettes have been introduced into the zone E they aresubjected to the reducing action of a current of gas contaning as anessential constituent carbon monoxde, said gas being supplied at T atthe inner end of the zone E from either of the recarbonizing furnaces Pand P for the time being heated byasupply of air as will be furtherexplained below. The gas may be preheated, if necessary, before itenters the zone E and its temperature may be about 1100 C. As thebriquettes already before their entrance into-the zone E have atemperature sufiiciently high for the reduction this process takes placeimmediately, the carbon monoxide of the gas supplied being partlyoxidized into carbon dioxide by the oxygen of the ore so that the latteris partly reduced.

By this prereduction the briquettes are re duced substantiallyintoferrous oxide (FeO) whereby the carbon monoxide is utilized in the mosteconomical manner and the carbon monoxide into carbon dioxide.

as when leaving the zone E will have a hi gh percentage of carbondioxide. The prereduction zone E is by means of a shutter a se aratedfrom the final reduction zone 0, sa1d shutter being momentarily openedwhen the carriages are moved forwards in the furnace.

In the final reduction zone 0 the briquettes are subjected to thereducing action of a current of carbon monoxide which is introduced at Gand taken out at H and the tem-v perature of which at the entrance maybe for instance 900 to 1000 C. As the briquettes still have a temperturesuitable for the performance of the reduction such process is continuedin the zone 0, the remaining oxygen of the ore being combined withsthcsa1 reaction continues until at the prevailing temperature acorresponding equilibrium is obtained between the carbon dioxide formedand the remaining carbon monoxide. By the continuous supply of carbonmonoxide at G the effect is obtained that the briquettes are subjectedto a as richer in carbon monoxide the nearer t ey come to the gas supplyG whereby a complete reduction is secured. Such reduction is alsofacilitated by the porosity of the briquettes and the intermediatespaces between them. It is not necessary to supply the circulatingcarbon monoxide at G inasmuch as a satisfactory re ducing effect can beobtained also when the gas is circulated in the opposite direction,

i. e. when the gas is supplied at H and taken out at G.

The performance of the process depends on the temperature which isobtained in the final reduction zone and the ratio of the carbon dioxideand carbon monoxide obtained in said zone. As the temperature of thebriquettes when they enter the zone 0 generally is about 1400 to 1450"C. but the reducing gas supplied to said zone has a lower temperaturethe temperature of the briquette is lowered as they are fed forwardsthrough the zone 0 while the temperature of the gases flowing in theopposite direction is raised. The excess of heat of the briquettes helpsthus to maintain the required temperature in the final reduction zone.If said excess of heat should not be sufficient to prevent a too eatfall of temperature in the final re uction zone the drawback would arisethat the carbon monoxide would be partly decomposed into free carbon andcarbon dioxide. Such draw back which may happen for instance whentreating easily fusible ores which cannot be preheated to a sufiicientlhigh temperature, can be removed by heat eing sup lied from an externalsource of heat to the al reduction zone.v For such purpose electricheating resistances K may be provided in the walls of said zone asindicated in Fig. 2 but also other heatin means may be used, as forinstance com ustion ases circulating through channels provided in saidwalls.

Thereducing as having passed through. the zone 0 is tal en out at H andsupplied to the recarbonizing furnaces P and P, which are filled with acharge of incandescent coke or other solid fuel. Said furnaces areoperated alternately in such manner that one is reheated while the otherdelivers its heat to the circulating gas for the endothermic reaction CO+C=2CO. A shiftable distribution valve L controls the quantities of gassupplied to either of the furnaces P and P By a shiftable valve Q, aircan be supplied to either of the recarbonizing furnaces and by means ofanother shiftable valve R the escaping gases can be supplied to thefinal reduction zone or to the prereduction zone at will.

\Vhen the valves Q, R are in the positions shown in Fig. 1, a portion ofthe circulating gas is introduced at the lower part of the furnace Ptogether with air. The su ply of air to said furnace is regulated m suchmanner that the carbon monoxide of the gas supplied to the furnace isonly partly combusted. Also the solid fuel is to some extent combustedpartly by direct combustion with the air supplied and partly by thecarbon dioxide of the gas taking up carbon so as to be converted intocarbon monoxide. In this manner the fuel charge in the furnace P isreheated to a high temperature. The carbon monoxide consumed for thereheating operation is partly covered by carbon monoxide formed from thefuel, so that the gas when escaping from the furnace P still has arather high percentage of carbon monoxide. The said gas is introduced inthe channel furnace at T and effects the prercduetion of the ore in thezone E, and is then combusted in the roasting zone D'as above described.The other portion of the gas taken out at H is introduced in the recarbonizing furnace P and is passed through its incandescent layer offuel which has previously been reheated as above described withreference to the furnace P When the reduction gas is passed through theincandescent carbon layer in the furnace P its content of carbon dioxideis reduced into carbon monoxide so that the gas escaping from saidrecarbonizing furnace consists, chiefly, of carbon monoxide whichthrough the valve R and a fan M or the like is returned to the channelfurnace at G.

The additional heat which is necessary for the reaction is taken fromthe heat accumulated in the incandescent fuel. When the temperature ofthe fuel has decreased in such degree that the formation of carbonmonoxide begins to cease the valves Q and R are reversed so that thefurnace P is disconnected from the circulation system and is setroasting operation, and all combustible gas forreheating While thefurnace P is con nected to the circulation system and delivers heat tothe circulating gas. For preventing the temperature of the circulatinggas from sinking too much a plurality of recarbonizing furnaces may beused in which case one always is connected to the circulation systemWhile the others are reheated. If desired, heat can be supplied to therecarbonizing furnace by electrical heating or in other man ner.Preferably, the electric energy is in formed in the process is fullyutilized.

The process can be regulated in several manners. The percentage ofcarbon monox: ide of the circulating gas can be regulated by regulatingthe speed of circulation and the quantity of circulating gas by means ofthe valve L. The percentage of carbon monoxide of the gas which issupplied to the roasting zone can be regulated by regulating thequantity of air supplied to the recarbonizing furnaces and the thicknessof fuel in such case supplied to the recarbonizing furthe latter. Thereduction time is regulated naces only during the reheating periods.Such supply of electric energy is suitable es pecially when an expensivefuel such as charcoal is used and the electric energy is cheap.

Before the recarbonized gas is introduced at G it can be conveyedthrough a heating apparatus S for raising its temperature in any desireddegree.

As above mentioned it is not necessary to conduct the reducing gasesthrough the final reduction zone G from G to H, i. e., in

counter-current to the movement of the loaded carriages inasmuch as thereducing effect will be practically the same if the reducing gases areconducted through the zone 0 from H to G, the piping from the valve Bbeing then connected to H and the piping from G being connected to thelower portions of the recarbonizing furnaces P and P In this latter casethe heatin apparatus S is, preferably, connected in the piping leadingfrom G to the furnaces P P in order to reheat the gases escaping fromthe final reduction zone before they enter the recarbonizing furnaces.

From the final reduction zone 0 the car riages are passed into coolingchambers N which are separated from the zone 0 and from each other byshutters d. In the first of said chambers the cooling preferably takesplace indirectly by means of air which is passed through pipings or thelike 6, Fig. 2, and then is supplied to the roasting zone D and utilizedfor the combustion of the gas supplied to said zone and, if desired,also to the recarbonizing furnaces. For the further cooling of thematerial pipings f, Fig. 2, supplied With cooling Water is used so thatthe spongy iron when taken out from the last cooling chamber issufiieiently cooled for preventing that any reoxidation thereof takesplace. The cooling should, preferably, take place in an atmosphere freefrom air or oxidizing gases and for this purpose some indifferent gas orgas mixture may be supplied to the cooling chambers.

The process above described gives a good economy inasmuch as thereduction is carried out immediately after the roasting while thebriquettes still have the high temperature which they have attainedduring the by the feeding of the carriages.

For facilitating the reduction the porosity of the briquettes can beincreased by mixing the ore with saw-dust, pulverulent charcoal or thelike, said addition being gasified in the preheating and roasting zonesleaving corresponding holes in the briquettes. Said additional fuel canalso to some extent by itself assist in effecting the reduction of theinner portions of the briquettes.

- The circulating gases can, of course, also contain hydrogen in agreater or less quantity. A gas containing hydrogen can for instance beobtained by supplying steam to the rccarbonizing furnaces during thereheating periods together With the circulating gas. The percentage ofhydrogen is regulated by regulating the supply of steam in relation tothe circulating gas supplied to the temporarily reheated furnace.

What I claim is 1. Method of reducing-ores, which comprises transportingthe ore successively in a substantially horizontal direction throughpreheating, roasting, prereduction and final reduction zones of achannel furnace, subjecting the ore in the final reduction zone to thereducing action of circulating reducing gases, recarbonizing said gasesoutside the channel furnace in alternately operative recarbonizingfurnaces, drawing off the exoess of circulating gases and partiallycombusting it in the momentarily inoperative recarbonizing furnace by aregulated supply of air for reheating said reca-rbonizing furnace,supplying the gases formed by said partial combustion to theprereduction zone of the channel furnace and finally combust ing them byan excess of air in the roasting zone.

2. Method of reducing ores, which comprises transporting the oresuccessively in a substantially horizontal direction through preheating,roasting, prereduction, final reduction and cooling zones of a channelfurnace, subjecting the ore in the final reduction zone to the reducingaction of circulating reducing gases, cooling the reduced ore indirectlyby means of air,'reca-rbon1z1ng the circulating gases outside thechannelfurnace in alternately operative recarbonizing furnaces, drawingoff the excess of circulating zone of t ing gases and partiallymomentarily inoperative recarbomzmg furnaoe by a regulated suppllylofair for reheating said recarbonizing rnace, supply ng the gases formedby said partial com ust on to the prereduction zone of the channelflirnace, and finally combusting them in the roasting zone of thechannel furnace b means of the hot air escaping from the coo ing zone.

3. Method of reducing ores, which comprises transporting the oresuccessively in a substantially horizontal direction through preheating,roasting, prereduction and final reduction zones of a channel furnace,subjecting the ore in the final reduction zone to the reducin action ofcirculatin reducing gases supp ied to said zone at t e inlet end for theore, recarbonizing said gases outside the channel furnace in alternatelyoperative recarbonizing furnaces, drawing off the excess of circulatinggases and partially combustin' it in the momentarily inoperative recarnizing furnace by a regulated supply of air for reheating saidrecarbonizing furnace, supplying the gases formed by said partialcombustion to the prereduction zone of the channel furnace, and finallycombusting them b an excess of air in the roasthe channel furnace so asto combusting it in the stantially horizontal direction throu h reaheating, roasting, prereduction, and ma reduction zones 0 a channelfurnace, subjecting the ore in the final reduction zone to the re ucingaction of circulating reducing gases, recarbonizing said gases outsidethe channel furnace in alternately o erative recarbonizing furnaces,drawing 0 the excess of circulating gases and partially combusting it inthe momentarily inoperative recarbonizing furnace by a regulated supplyof air for reheating said recarbonizing furnace sup lying the gasesformed by said partial com ustion to the 'prereduction zone of thechannel furnace and finally oombusting them together with the fuel mixedwith ore by an excess of air in theroasting zone of the channel furnaceso as to roast the ore and heat it to a temperature above that necessaryfor the reduction.

In testimony whereof I have signed my name. 4

BROR CHRISTIAN SEN.

